Chain disorder with frustration can modify the universality class of scaling at the theta transition of heteropolymers. This is shown for a model with random two-body potentials in 2D on the basis of exact enumeration and accurate Monte Carlo results. When the average fraction of repulsive monomer-monomer interactions grows beyond a certain finite threshold, the temperature below which disorder becomes relevant coincides with the theta one, and scaling exponents definitely start deviating from those valid For homopolymers.